Catalytic wet oxidation systems and methods

ABSTRACT

A system and method for the treatment of process streams. A catalyst mediates a wet oxidation process at elevated temperatures and pressures for treating at least one undesirable constituent in an aqueous mixture. A catalyst may be selected for its solubility at a detected pH level of the aqueous mixture. Alternatively, a pH level of the aqueous mixture may be adjusted to solubilize a selected catalyst and/or maintain the selected catalyst in a soluble form. A controller in communication with a pH sensor may be configured to generate a control signal to adjust the pH level of the aqueous mixture in response to the pH sensor registering a pH level outside a predetermined pH solubility range for a selected catalyst.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the treatment of processstreams and, more particularly, to catalytic wet oxidation systems andmethods for treatment of undesirable constituents therein.

2. Description of Related Art

Wet oxidation is a well-known technology for treating process streams,and is widely used, for example, to destroy pollutants in wastewater.The method involves aqueous phase oxidation of undesirable constituentsby an oxidizing agent, generally molecular oxygen from anoxygen-containing gas, at elevated temperatures and pressures. Theprocess can convert organic contaminants to carbon dioxide, water andbiodegradable short chain organic acids, such as acetic acid. Inorganicconstituents including sulfides, mercaptides and cyanides can also beoxidized. As an alternative to incineration, wet oxidation may be usedin a wide variety of applications to treat process streams forsubsequent discharge, in-process recycle, or as a pretreatment step tosupply a conventional biological treatment plant for polishing.Catalytic wet oxidation has emerged as an effective enhancement totraditional non-catalytic wet oxidation. Catalytic wet oxidationprocesses generally allow for greater destruction to be achieved at alower temperature and pressure, and therefore a lower capital cost. Anaqueous stream to be treated is mixed with an oxidizing agent andcontacted with a catalyst at elevated temperatures and pressures.Heterogeneous catalysts typically reside on a bed over which the aqueousmixture is passed, or in the form of solid particulate which is blendedwith the aqueous mixture prior to oxidation. The catalyst may befiltered out of the oxidation effluent downstream of the wet oxidationunit for reuse.

BRIEF SUMMARY OF THE INVENTION

In accordance with one or more embodiments, the invention relates to acatalytic wet oxidation process. The process may comprise providing anaqueous mixture containing at least one undesirable constituent to betreated, detecting a pH level of the aqueous mixture, selecting acatalyst based on the detected pH level of the aqueous mixture, andcontacting the aqueous mixture with the selected catalyst and anoxidizing agent at an elevated temperature and a superatmosphericpressure to treat the at least one undesirable constituent.

In accordance with one or more embodiments, the invention relates to acatalytic wet oxidation process. The process may comprise providing anaqueous mixture containing at least one undesirable constituent to betreated, selecting a catalyst, detecting a pH level of the aqueousmixture, adjusting the pH level of the aqueous mixture based on theselected catalyst, and contacting the aqueous mixture with the selectedcatalyst and an oxidizing agent at an elevated temperature and asuperatmospheric pressure to treat the at least one undesirableconstituent.

In accordance with one or more embodiments, the invention relates to acatalytic wet oxidation system. The system may comprise a wet oxidationunit, a source of an aqueous mixture comprising at least one undesirableconstituent fluidly connected to the wet oxidation unit, a pH sensorconfigured to detect a pH level of the aqueous mixture, and a source ofa catalyst soluble in the aqueous mixture fluidly connected to the wetoxidation unit, positioned between the source of the aqueous mixture andthe wet oxidation unit.

In accordance with one or more embodiments, the invention relates to amethod of facilitating a catalytic wet oxidation process, comprisingproviding a pH monitoring system having a controller in communicationwith a pH sensor, the controller configured to generate a control signalto adjust a pH level of an aqueous mixture in response to the pH sensorregistering a pH level outside a predetermined pH solubility range for autilized catalyst.

Other advantages, novel features and objects of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. Preferred, non-limiting embodiments of the present inventionwill be described with reference to the accompanying drawings, in which:

FIG. 1 is a system diagram in accordance with one embodiment of the wetoxidation system of the present invention; and

FIGS. 2-4 are Pourbaix diagrams referenced herein for copper, vanadium,and iron, respectively.

DETAILED DESCRIPTION OF THE INVENTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components as set forth in thefollowing description or illustrated in the drawings. The invention iscapable of embodiments and of being practiced or carried out in variousways beyond those exemplarily presented herein.

In accordance with one or more embodiments, the invention relates to oneor more systems and methods for treating process streams. In typicaloperation, the disclosed systems may receive process streams fromcommunity, industrial or residential sources. For example, inembodiments in which the system is treating wastewater, the processstream may be delivered from a municipal wastewater sludge or otherlarge-scale sewage system. Process streams may also originate, forexample, from food processing plants, chemical processing facilities,gasification projects, or pulp and paper plants. The process stream maybe moved through the system by an operation upstream or downstream ofthe system.

As used herein, the term “process stream” refers to an aqueous mixturedeliverable to the system for treatment. After treatment, the processstream may be returned to an upstream process or may exit the system aswaste. The aqueous mixture typically includes at least one undesirableconstituent capable of being oxidized. The undesirable constituent maybe any material or compound targeted to be removed from the aqueousmixture, such as for public health, process design and/or aestheticconsiderations. In some embodiments, the undesirable constituentscapable of being oxidized are organic compounds. Certain inorganicconstituents, for example, sulfides, mercaptides and cyanides can alsobe oxidized. A source of an aqueous mixture to be treated by the system,such as a slurry, may take the form of direct piping from a plant orholding vessel.

In accordance with one or more embodiments of the present invention, itis desirable to disrupt one or more specific chemical bonds in theundesirable constituent or degradation product(s) thereof. An oxidationreaction is one destruction technique, capable of converting oxidizableorganic contaminants to carbon dioxide, water and biodegradable shortchain organic acids, such as acetic acid. One aspect of the presentinvention involves systems and methods for oxidative treatment ofaqueous mixtures containing one or more undesirable constituents.

In one embodiment, an aqueous mixture including at least one undesirableconstituent is wet oxidized. The aqueous mixture is oxidized with anoxidizing agent at an elevated temperature and superatmospheric pressurefor a duration sufficient to treat the at least one undesirableconstituent. The oxidation reaction may substantially destroy theintegrity of one or more chemical bonds in the undesirable constituent.As used herein, the phrase “substantially destroy” is defined as atleast about 95% destruction. The process of the present invention isgenerally applicable to the treatment of any undesirable constituentcapable of being oxidized.

The disclosed wet oxidation processes may be performed in any knownbatch or continuous wet oxidation unit suitable for the compounds to beoxidized. Typically, aqueous phase oxidation is performed in acontinuous flow wet oxidation system, as exemplarily shown in FIG. 1.Any oxidizing agent may be used. The oxidant is usually anoxygen-containing gas, such as air, oxygen-enriched air, or essentiallypure oxygen. As used herein, the phrase “oxygen-enriched air” is definedas air having an oxygen content greater than about 21%.

In typical operation, and with reference to FIG. 1, an aqueous mixturefrom a source, shown as storage tank 10, flows through a conduit 12 to ahigh pressure pump 14 which pressurizes the aqueous mixture. The aqueousmixture is mixed with a pressurized oxygen-containing gas, supplied by acompressor 16, within a conduit 18. The aqueous mixture flows through aheat exchanger 20 where it is heated to a temperature which initiatesoxidation. The heated feed mixture then enters a reactor vessel 24 atinlet 38. The wet oxidation reactions are generally exothermic and theheat of reaction generated in the reactor may further raise thetemperature of the mixture to a desired value. The bulk of the oxidationreaction occurs within reactor vessel 24 which provides a residence timesufficient to achieve the desired degree of oxidation. The oxidizedaqueous mixture and oxygen depleted gas mixture then exit the reactorthrough a conduit 26 controlled by a pressure control valve 28. The hotoxidized effluent traverses the heat exchanger 20 where it is cooledagainst incoming raw aqueous mixture and gas mixture. The cooledeffluent mixture flows through a conduit 30 to a separator vessel 32where liquid and gases are separated. The liquid effluent exits theseparator vessel 32 through a lower conduit 34 while off gases arevented through an upper conduit 36. Treatment of the off gas may berequired in a downstream off gas treatment unit depending on itscomposition and the requirements for discharge to the atmosphere. Thewet oxidized effluent may typically be discharged into a biologicaltreatment plant for polishing. The effluent may also be recycled forfurther processing by the wet oxidation system.

Sufficient oxygen-containing gas is typically supplied to the system tomaintain residual oxygen in the wet oxidation system off gas, and thesuperatmospheric gas pressure is typically sufficient to maintain waterin the liquid phase at the selected oxidation temperature. For example,the minimum system pressure at 240° C. is 33 atmospheres, the minimumpressure at 280° C. is 64 atmospheres, and the minimum pressure at 373°C. is 215 atmospheres. In one embodiment, the aqueous mixture isoxidized at a pressure of about 30 atmospheres to about 275 atmospheres.The wet oxidation process may be operated at an elevated temperaturebelow 374° C., the critical temperature of water. In some embodiments,the wet oxidation process may be operated at a supercritical elevatedtemperature. The retention time for the aqueous mixture within thereaction chamber should be generally sufficient to achieve the desireddegree of oxidation. In some embodiments, the retention time is aboveabout one hour and up to about eight hours. In at least one embodiment,the retention time is at least about 15 minutes and up to about 6 hours.In one embodiment, the aqueous mixture is oxidized for about 15 minutesto about 4 hours. In another embodiment, the aqueous mixture is oxidizedfor about 30 minutes to about 3 hours.

According to one or more embodiments, the wet oxidation process is acatalytic wet oxidation process. The oxidation reaction may be mediatedby a catalyst. The aqueous mixture containing at least one undesirableconstituent to be treated is generally contacted with a catalyst and anoxidizing agent at an elevated temperature and superatmosphericpressure. An effective amount of catalyst may be generally sufficient toincrease reaction rates and/or improve the overall destruction removalefficiency of the system, including enhanced reduction of chemicaloxygen demand (COD) and/or total organic carbon (TOC). The catalyst mayalso serve to lower the overall energy requirements of the wet oxidationsystem.

In at least one embodiment, the catalyst may be any transition metal ofgroups V, VI, VII and VIII of the Periodic Table. In one embodiment, forexample, the catalyst may be V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, oralloys or mixtures thereof. The transition metal may be elemental orpresent in a compound, such as a metal salt. In one embodiment, thetransition metal catalyst is vanadium. In another embodiment, thetransition metal catalyst is iron. In yet another embodiment, thetransition metal catalyst is copper.

A catalyst may be added to the aqueous mixture at any point in the wetoxidation system. The catalyst may be mixed with the aqueous mixture. Inone embodiment, the catalyst may be added to the source of the aqueousmixture feeding the wet oxidation unit as illustrated in FIG. 1 in whichcatalyst source 40 is fluidly connected to storage tank 10. In someembodiments, the catalyst may be directly added to the wet oxidationunit. In other embodiments, the catalyst may also be supplied to theaqueous mixture prior to heating and/or pressurization.

In yet other embodiments, the catalyst may already be present in theprocess stream to be treated. The aqueous mixture supplied to theoxidation unit may contain a catalytic material. For example, transitionmetals may be present in a waste stream to be treated by the catalyticwet oxidation system. Aqueous slurries, such as those containingvolatile organic carbons, may contain metals capable of acting as acatalyst. For example, the aqueous mixture may be a slurry ofgasification byproducts.

According to one or more embodiments, the catalyst may be soluble in theaqueous mixture to enhance the wet oxidation process. In general,characteristics of the aqueous mixture may impact the solubility of acatalyst in the aqueous mixture. For example, a pH level of the aqueousmixture to be treated may affect the solubility of a particular catalystin the aqueous mixture.

In some embodiments, a catalyst may be selected based on acharacteristic of the aqueous mixture. As illustrated in FIG. 1, the wetoxidation system may include a sensor 50, configured to detect acharacteristic of the aqueous mixture to be treated. In someembodiments, sensor 50 may be a pH sensor configured to detect a pHlevel of the aqueous mixture, and a catalyst for the wet oxidationprocess may be selected based on a detected pH level of the aqueousmixture.

The relationship between solubility and pH level for various catalystsis generally known by those skilled in the art. Potential-pH equilibriumdiagrams have been constructed for various catalyst-water systems andare readily available to those skilled in the art familiar with how toreference them. For example, reproductions of what are commonly referredto as Pourbaix diagrams available from Pourbaix, M. M., The Atlas ofElectrochemical Equilibria in Aqueous Solutions, National Association ofCorrosion Engineers: Texas 1974, are presented in FIGS. 2-4 for copper,vanadium and iron, respectively.

In accordance with one or more embodiments, a catalyst soluble at thedetected pH level may be selected to enhance the wet oxidation process.Thus, with reference to FIG. 2, if the pH level of the aqueous mixturedetected by pH sensor 50 is below about 2 or above about 13, a catalystcomprising copper may be selected for catalyst source 40 in accordancewith one or more embodiments. Likewise, with reference to FIG. 3, acatalyst comprising vanadium may be selected when the detected pH levelis above about 4.5. With reference to FIG. 4, a catalyst comprising ironmay be selected when the detected pH level is below about 4. Othercatalysts beyond those exemplarily presented herein may be utilized.

In other embodiments, a catalyst may be selected and one or morecharacteristics of the aqueous mixture may be manipulated to promote thepresence of the selected catalyst in a soluble form to enhance the wetoxidation process. For example, a pH level of the aqueous mixture may bedetected by sensor 50 and adjusted to solubilize the selected catalystin the aqueous mixture. A pH adjuster may be added to the aqueousmixture at any point within the wet oxidation system but is preferablyadded such that the catalyst is soluble within the aqueous mixtureduring the oxidation reaction. In some embodiments, a source of pHadjuster 60 may be fluidly connected to the source of the aqueousmixture 10 as illustrated in FIG. 1. The source of pH adjuster 60 maygenerally include any material or compound capable of adjusting the pHlevel of the aqueous mixture to a desired value or range, such as anacid or base. For example, an alkali metal hydroxide may be utilized toadjust the pH level of the aqueous mixture. In one embodiment, ammoniamay be used to solubilize the catalyst.

Again, the relationship between solubility and pH level for variouscatalysts is generally known by those skilled in the art. As discussedabove, Pourbaix diagrams may provide information for determining adesired pH range in which a selected catalyst would be soluble. Withreference to FIG. 2, the pH level of the aqueous mixture may be adjustedto below about 2 or above about 13 when the selected catalyst comprisescopper. Likewise, with reference to FIG. 3, the pH level of the aqueousmixture may be adjusted to above about 4.5 when the selected catalystcomprises vanadium. When a catalyst comprising iron is selected, the pHlevel of the aqueous mixture may be adjusted to a level below about 4with reference to FIG. 4.

In some embodiments, the wet oxidation system may include a controller70 for adjusting or regulating at least one operating parameter of thesystem or a component of the system, such as, but not limited to,actuating valves and pumps. Controller 70 may be in electroniccommunication with sensor 50 as illustrated in FIG. 1. Controller 70 maybe generally configured to generate a control signal to adjust the pHlevel of the aqueous mixture in response to the pH sensor 50 registeringa pH level outside a predetermined pH solubility range for the selectedcatalyst. For example, controller 70 may provide a control signal to oneor more valves associated with pH adjuster source 60 to add pH adjusterto aqueous mixture source 10.

The controller 70 is typically a microprocessor-based device, such as aprogrammable logic controller (PLC) or a distributed control system,that receives or sends input and output signals to and from componentsof the wet oxidation system. Communication networks may permit anysensor or signal-generating device to be located at a significantdistance from the controller 70 or an associated computer system, whilestill providing data therebetween. Such communication mechanisms may beeffected by utilizing any suitable technique including but not limitedto those utilizing wireless protocols.

As discussed above with respect to typical operation of the oxidationunit, a liquid effluent is separated from the oxidized aqueous mixturedownstream of the oxidation reactor. In some embodiments, the catalystmay be recovered from the liquid effluent by a separation process. Forexample, in some embodiments the catalyst may be precipitated out of theeffluent stream. In one embodiment, a crystallizer may be used torecover the catalyst. The catalyst may then be recycled back to the wetoxidation system.

According to one or more embodiments, the wet oxidized liquid effluentstream may be processed by a secondary treatment unit 80 connecteddownstream of the oxidation reactor vessel 24 to remove remainingundesirable constituents present and/or polish when necessitated ordesired. The secondary treatment unit 80 may be a chemical scrubber, abiological scrubber, an adsorption media bed, or other unit operation.In some embodiments, an advanced oxidation step including oxidationtreatment of the wet oxidation effluent with ozone and ultraviolet lightmay be performed. Such advanced oxidation treatment is typically carriedout in a vessel or tank at or near ambient temperature and pressure. Thesecondary treatment unit 80 may be sized to provide a surface areaconsistent with the desired degree of polishing. Alternatively, theliquid effluent may also be recycled back to reactor vessel 24 forfurther processing. Treatment of the off gas may also be required in adownstream off gas treatment unit depending on its composition and therequirements for discharge to the atmosphere.

Sensors to detect a concentration of a targeted odorous constituent maybe provided upstream and/or downstream of the wet oxidation unit 24 tofacilitate system control. For example, a sensor may be positioned atconduit 26 and be in communication with controller 70 to determineand/or control whether the liquid effluent stream should be diverted tothe secondary treatment unit 80 to meet established environmentalregulations.

It should be appreciated that numerous alterations, modifications andimprovements may be made to the illustrated systems and methods. Forexample, one or more wet oxidation systems may be connected to multiplesources of process streams. In some embodiments, the wet oxidationsystem may include additional sensors for measuring other properties oroperating conditions of the system. For example, the system may includesensors for temperature, pressure drop, and flow rate at differentpoints to facilitate system monitoring. In accordance with one or moreembodiments, the catalyst may be replenished during the wet oxidationprocess.

The invention contemplates the modification of existing facilities toretrofit one or more systems or components in order to implement thetechniques of the invention. An existing wet oxidation system can bemodified in accordance with one or more embodiments exemplarilydiscussed herein utilizing at least some of the preexisting equipment.For example, one or more pH sensors may be provided and a controller inaccordance with one or more embodiments presented herein may beimplemented in a preexisting wet oxidation system to promote catalystsolubility.

The function and advantages of these and other embodiments of thepresent invention will be more fully understood from the followingexamples. These examples are intended to be illustrative in nature andare not considered to be limiting the scope of the invention. In thefollowing examples, compounds are treated by wet oxidation to affectdestruction of bonds therein.

EXAMPLES Bench Scale Wet Oxidation (Autoclave) Reactors

In the following Examples, bench scale wet oxidation tests wereperformed in laboratory autoclaves. The autoclaves differ from the fullscale system in that they are batch reactors, where the full scale unitmay be a continuous flow reactor. The autoclaves typically operate at ahigher pressure than the full scale unit, as a high charge of air mustbe added to the autoclave in order to provide sufficient oxygen for theduration of the reaction. The results of the autoclave tests provide anindication of the performance of the wet oxidation technology and areuseful for screening operating conditions for the wet oxidation process.

The autoclaves used were fabricated from titanium, alloy 600 and Nickel200. The selection of the autoclave material of construction was basedon the composition of the wastewater feed material. The autoclavesselected for use, each have total capacities of 500 or 750 ml.

The autoclaves were charged with wastewater and sufficient compressedair to provide excess residual oxygen following the oxidation (ca. 5%).The charged autoclaves were placed in a heater/shaker mechanism, heatedto the desired temperature (280° C. to 350° C.) and held at temperaturefor the desired time, ranging from about 60 minutes to about 360minutes.

During the heating and reacting periods, the autoclave temperature andpressure were monitored by a computer controlled data acquisitionsystem. Immediately following oxidation, the autoclaves were removedfrom the heater/shaker mechanism and cooled to room temperature usingtap water. After cooling, the pressure and volume of the off gas in theautoclave head-space were measured. A sample of the off-gas was analyzedfor permanent gases. Subsequent to the analysis of the off gas, theautoclave was depressurized and opened. The oxidized effluent wasremoved from the autoclave and placed into a storage container. Aportion of the effluent was submitted for analysis and the remainingsample was used for post-oxidative treatment. In order to generatesufficient volume for analytical work and post-oxidation test work,multiple autoclave tests for each condition were run.

Example 1 Wet Oxidation Process Utilizing a Homogeneous Copper Catalyst

Bench scale wet oxidation tests were performed at 280° C. with a 60minute time at temperature to determine the impact of a copper catalyston the oxidation of acetic acid at various pH levels (pH=2.2, 8.1, 11.5,12.5 and 13.5). The data is presented below in Table 1.

TABLE 1 Results from wet oxidation (WO) of an acetic acid solution usingcopper catalyst. 10 g/L Wet oxidation at 280° C. - 60 minutes AceticEffluent Effluent Effluent Effluent Effluent Acid pH = pH = pH = pH = pH= Feed 2.2 8.1 11.5 12.5 13.5 Charge Conditions Autoclave Material — — —Ti Ti Ni 200 Ni 200 INC 600 Autoclave Volume ml — — 500 500 500 500 750Volume of Liquid ml — — 150 100 100 100 200 Charged Copper Concentrationg/L Cu — 1 1 1 1 0.5 NaOH Charged g/L NaOH — 0 7 1.2 1.6 20 Air Chargedpsig — — 310 200 200 200 260 Oxidation ° C. — — 280 280 280 280 280Temperature Time at Temperature min — — 60 60 60 60 60 Reported asAnalysis Results M. COD mg/L O2 10100 356 7300 7300 6960 1180 % CODDestruction — — — 96.5 27.7 27.7 31.1 90 TOC mg/L C  3950 141 2790 27902750 485.0 % TOC Destruction — — — 96.4 29.4 29.4 30.4 88.1 SolubleCopper mg/L Cu — 633 1.04 <0.1 0.18 84.5 pH — — — 2.20 8.13 11.46 12.5013.5 Organic Acids Acetic Acid mg/L CH₃COOH 10050 222 8390 7270 64801260 % Acetic Acid % — — 97.8 16.5 27.7 35.5 87.5 Destruction

The copper catalyst exhibited the highest solubility at pH levels of 2.2and 13.5. When the pH of the oxidized effluent was 2.2 and 13.5, about98% and 88% acetic acid destruction was achieved, respectively. Thisalso corresponded to the highest percentages of COD destruction (96.5%,90%) and TOC destruction (96.4%, 88.1%). In contrast, when the pH of thesolution was maintained in the pH range where copper was not soluble(pH=8.1, 11.5 and 12.5) only about 17% to 37% acetic acid destructionwas achieved. When the copper was not soluble, lower percentages of CODdestruction and TOC destruction were observed as well. The dataindicated that copper solubility substantially increased the oxidationof acetic acid.

Example 2 Wet Oxidation Process Utilizing a Homogeneous VanadiumCatalyst

Bench scale wet oxidation tests were performed on a water solutioncontaining acetic acid using vanadium as a homogeneous catalyst at twodifferent pH levels. The results are presented in Table 2 below.

TABLE 2 Results from wet oxidation of an acetic acid solution using avanadium catalyst. Without With Without With Catalyst Catalyst CatalystCatalyst 10 g/L WO at WO at WO at WO at Acetic 280° C., 280° C., 280°C., 280° C., Acid 60 60 60 60 Feed for minutes, minutes, minutes,minutes, V Runs pH = 2.7 pH = 2.7 pH = 6.5 pH = 5.3 Lims 197268 188294197271 188420 197272 Book Ref 2790-26-1 2751-88-1 2790-29-1 2751-91-12790-30-1 Charge Conditions Autoclave Material — — — Ti Ti Ti TiAutoclave Volume ml — — 500 500 500 500 Volume of Liquid ml — — 150 150150 150 Charged Vanadium mg/L V — 0 5000 0 5000 Concentration NaOHCharged g/L NaOH — 0 0 6.8 6.8 Air Charged psig — — 300 300 300 300Oxidation Temperature ° C. — — 280 280 280 280 Time at Temperature min —— 60 60 60 60 Reported Analysis Results as TOC mg/L C 3741 3710 33303790 3093 % TOC Destruction — — — 2 11.0 5.3 17.3 pH — — 2.6 2.66 6.505.29

Under oxidative conditions, vanadium is soluble at pH levels greaterthan about 4.5. The results show that when the pH of the solution was2.6, and the vanadium was mostly insoluble, only 2% destruction of TOCwas achieved. A low percentage of TOC destruction was associated with apH level of 2.66 as well. When the pH of the solution was increased to5.3 (solubilizing the vanadium), while maintaining the same catalystdosage, temperature, and time at temperature the destruction of TOC wasincreased to 17.3%. By increasing the pH of the solution from 2.66 to5.3, there was about a 64% increase in the destruction of total organiccarbon. The data indicated that vanadium solubility substantiallyincreased the oxidation of acetic acid.

Example 3 Wet Oxidation Process Utilizing a Homogeneous Iron Catalyst

Bench scale wet oxidation tests were performed at 230° C. for 150minutes on an oxalic acid solution at two different pH levels. The datais presented in Table 3 below.

TABLE 3 Results from wet oxidation of an oxalic acid solution using aniron catalyst. Feed High High Low Low Reported 18 g/L pH, no pH, Fe pH,no pH, Fe Units As Oxalate catalyst Catalyst catalyst Catalyst ChargeConditions Autoclave Material — — — Inc 600 Inc 600 Ti Ti AutoclaveVolume ml — — 750 750 500 500 Volume of Liquid Charged ml — — 250 250200 200 Air Charged psig — — 520 520 440 440 Oxidation Temperature ° C.— — 230 230 230 230 Time at Temperature min — — 150 150 150 150 Fe + 2added (as FeSO₄) g/L Fe — — 2.24 — 2.24 Analysis Results TOC mg/L C 51003650 3720 240.0 <5.6 TOC Destruction % — — 28.4 27.1 95.3 99.9 DIC mg/LC <20 955 912.0 — — pH — — 13.7 13.7 13.6 2.6 1.7

Under oxidative conditions, iron is soluble below a pH level of about 4.The results indicated that there was no enhancement of oxidation when aniron catalyst was used at a high pH level (pH=13.6 and 13.7) where itwas insoluble. When the pH of the solution was in the range where theiron was soluble (pH=2.6 and 1.7), the destruction of oxalic acid wasincreased to about 95% and about 100%, respectively. The data indicatedthat iron solubility substantially increased the oxidation of oxalicacid.

Example 4 Wet Oxidation of Chlorophenol Utilizing a Homogeneous IronCatalyst

Both iron catalyzed and non-catalyzed oxidations of chlorophenol wereperformed at 150° C. with a 90 minute time at temperature. The data istabulated below in Table 4.

TABLE 4 Results from wet oxidation of chlorophenol using an ironcatalyst. WO of Chlorophenol (1.24 g/L) Units Reported As Feed NoCatalyst Fe Catalyst LIMS 182594 182595 182596 Book Ref 2751-51-12751-82-1 2751-83-1 Charge Conditions Autoclave Material — — — Ti TiAutoclave Volume ml — — 500 500 Volume of Liquid Charged ml — — 200 200Air Charged psig — — 200 200 Oxidation Temperature ° C. — — 150 150 Timeat Temperature min — — 90 90 Fe Catalyst added g/L FeSO₄7H₂O — — 0.5Analysis Results M. COD mg/L O2 2040 1890 650 COD Destruction % — — 7.468.1 TOC mg/L C 667 620 284 TOC Destruction % — — 7.0 57 Sol Fe mg/L Fe— — 48 pH — — 5.4 2.90 2.30

These tests showed that increasing the solubility of the iron catalyst,by lowering the pH level from 2.9 to 2.3, resulted in increasing TOCdestruction from about 7% to about 57%. Likewise, lowering the pH levelincreased COD destruction from about 7.4% to about 68.1%. The dataindicated that even slight adjustment of pH level significantlyincreases the efficiency of a catalytic wet oxidation process.

As used herein, the term “plurality” refers to two or more items orcomponents. The terms “comprising,” “including,” “carrying,” “having,”“containing,” and “involving,” whether in the written description or theclaims and the like, are open-ended terms, i.e., to mean “including butnot limited to.” Thus, the use of such terms is meant to encompass theitems listed thereafter, and equivalents thereof, as well as additionalitems. Only the transitional phrases “consisting of” and “consistingessentially of,” are closed or semi-closed transitional phrases,respectively, with respect to the claims.

Use of ordinal terms such as “first,” “second,” “third,” and the like inthe claims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Those skilled in the art should appreciate that the parameters andconfigurations described herein are exemplary and that actual parametersand/or configurations will depend on the specific application in whichthe systems and techniques of the invention are used. Those skilled inthe art should also recognize, or be able to ascertain, using no morethan routine experimentation, equivalents to the specific embodiments ofthe invention. It is therefore to be understood that the embodimentsdescribed herein are presented by way of example only and that, withinthe scope of the appended claims and equivalents thereto; the inventionmay be practiced otherwise than as specifically described.

1. A catalytic wet oxidation process, comprising: providing an aqueousmixture containing at least one undesirable constituent to be treated;detecting a pH level of the aqueous mixture; selecting a catalyst basedon the detected pH level of the aqueous mixture; and contacting theaqueous mixture with the selected catalyst and an oxidizing agent at anelevated temperature and a superatmospheric pressure to treat the atleast one undesirable constituent.
 2. The process according to claim 1,wherein selecting the catalyst comprises selecting a catalyst soluble atthe detected pH level.
 3. The process according to claim 1, whereinselecting the catalyst comprises selecting a transition metal catalyst.4. The process according to claim 3, wherein selecting the catalystcomprises selecting a catalyst comprising copper when the detected pHlevel is below about
 2. 5. The process according to claim 3, whereinselecting the catalyst comprises selecting a catalyst comprising copperwhen the detected pH level is above about
 13. 6. The process accordingto claim 3, wherein selecting the catalyst comprises selecting acatalyst comprising vanadium when the detected pH level is above about4.5.
 7. The process according to claim 3, wherein selecting the catalystcomprises selecting a catalyst comprising iron when the detected pHlevel is below about
 4. 8. The process according to claim 2, whereincontacting the aqueous mixture with the selected catalyst occurs priorto heating.
 9. The process according to claim 2, wherein contacting theaqueous mixture with the selected catalyst occurs prior topressurization.
 10. The process according to claim 1, further comprisingmonitoring the pH level of the aqueous mixture.
 11. The processaccording to claim 1, wherein the aqueous mixture is oxidized in acontinuous process.
 12. The process according to claim 11, furthercomprising replenishing the catalyst.
 13. The process according to claim1, wherein contacting the aqueous mixture with an oxidizing agentcomprises contacting the aqueous mixture with an oxygen-containing gas.14. The process according to claim 1, further comprising recovering thecatalyst.
 15. The process according to claim 14, wherein recovering thecatalyst involves precipitating the catalyst.
 16. The process accordingto claim 1, wherein the aqueous mixture is oxidized for a period of timesufficient to treat the at least one undesirable constituent.
 17. Theprocess according to claim 1, wherein the superatmospheric pressure isfrom about 30 atmospheres to about 275 atmospheres.
 18. The processaccording to claim 1, wherein the elevated temperature is from about240° C. to about the critical temperature of water.
 19. The processaccording to claim 1, wherein the elevated temperature is above thecritical temperature of water.
 20. A catalytic wet oxidation process,comprising: providing an aqueous mixture containing at least oneundesirable constituent to be treated; selecting a catalyst; detecting apH level of the aqueous mixture; adjusting the pH level of the aqueousmixture based on the selected catalyst; and contacting the aqueousmixture with the selected catalyst and an oxidizing agent at an elevatedtemperature and a superatmospheric pressure to treat the at least oneundesirable constituent.
 21. The process according to claim 20, whereinadjusting the pH level comprises adjusting the pH level of the aqueousmixture to solubilize the selected catalyst.
 22. The process accordingto claim 20, wherein adjusting the pH level comprises adjusting the pHlevel of the aqueous mixture to maintain the catalyst in a soluble form.23. The process according to claim 20, wherein adjusting the pH levelcomprises utilizing an alkali metal hydroxide.
 24. The process accordingto claim 20, wherein selecting the catalyst comprises selecting atransition metal catalyst.
 25. The process according to claim 24,wherein adjusting the pH level comprises adjusting the pH level to belowabout 2 when the selected catalyst comprises copper.
 26. The processaccording to claim 24, wherein adjusting the pH level comprisesadjusting the pH level to above about 13 when the selected catalystcomprises copper.
 27. The process according to claim 24, whereinadjusting the pH level comprises adjusting the pH level to above about4.5 when the selected catalyst comprises vanadium.
 28. The processaccording to claim 24, wherein adjusting the pH level comprisesadjusting the pH level to below about 4 when the selected catalystcomprises iron.
 29. The process according to claim 20, wherein theaqueous mixture is oxidized for a period of time sufficient to treat theat least one undesirable constituent.
 30. The process according to claim29, wherein the superatmospheric pressure is from about 30 atmospheresto about 275 atmospheres.
 31. The process according to claim 29, whereinthe elevated temperature is from about 240° C. to about the criticaltemperature of water.
 32. The process according to claim 29, wherein theelevated temperature is above the critical temperature of water.
 33. Theprocess according to claim 20, wherein the aqueous mixture is oxidizedin a continuous process.
 34. The process according to claim 33, furthercomprising replenishing the catalyst.
 35. The process according to claim20, wherein selecting the catalyst comprises selecting a catalystpresent in the aqueous mixture.
 36. The process according to claim 20,further comprising recovering the catalyst.
 37. A catalytic wetoxidation system, comprising: a wet oxidation unit; a source of anaqueous mixture comprising at least one undesirable constituent fluidlyconnected to the wet oxidation unit; a pH sensor configured to detect apH level of the aqueous mixture; and a source of a catalyst soluble inthe aqueous mixture fluidly connected to the wet oxidation unit,positioned between the source of the aqueous mixture and the wetoxidation unit.
 38. The system of claim 37, wherein the catalyst isselected to be soluble at the detected pH level.
 39. The system of claim37, further comprising a secondary treatment unit connected downstreamof the wet oxidation unit.
 40. The system of claim 37, furthercomprising a controller in communication with the pH sensor, configuredto generate a control signal to adjust the pH level of the aqueousmixture in response to the pH sensor registering a pH level outside apredetermined pH solubility range for the catalyst.
 41. A method offacilitating a catalytic wet oxidation process, comprising: providing apH monitoring system having a controller in communication with a pHsensor, the controller configured to generate a control signal to adjusta pH level of an aqueous mixture in response to the pH sensorregistering a pH level outside a predetermined pH solubility range for autilized catalyst.